Friday, November 30, 2012

The
structural features of quinone ligands are diagnostic of charge. The
o-benzoquinone, radical semiquinonate, and catecholate electronic forms have
C−O bond lengths and a pattern of ring C−C bond lengths that point to a
specific mode of coordination. This correlation between ligand charge and
structure has been extended to iminoquinone and iminothioquinone ligands,
giving a charge-localized view of electronic structure for complexes of
redox-active metal ions. The radical semiquinonate form of these ligands has
been found to be a surprisingly common mode of coordination; however, the
paramagnetic character of the radical ligand is often obscured in complexes
containing paramagnetic metal ions. In this report, diamagnetic
iminosemiquinonate (isq) and iminothiosemiquinonate (itsq) complexes of ls-d5
Ru(III) with related complexes of osmium are reported. With osmium, the
Os(IV)−amidophenolate (ap) redox isomer is formed. Electrochemical and spectral
properties are described for Ru(PPh3)2(isq)Cl2, Ru(PPh3)2(itsq)Cl2,
Os(PPh3)2(ap)Br2, Os(PPh3)2(atp)Br2, and Os(PPh3)2(ap)H2. Crystallographic
characterization of Ru(PPh3)2(isq)Cl2, Ru(PPh3)2(itsq)Cl2, and Os(PPh3)2(ap)H2
was used to assign charge distributions.